Most vehicle seats include a framework consisting of two frames articulated to one another, one for the seat part of the seat, the other for the backrest of the seat.
Furthermore, in some cases, the framework of the backrest of the seat itself consists of two frames articulated to one another, as illustrated, for example, in the document U.S. Pat. No. 4,626,028.
In all cases, these pivoting mounts must be particularly strong to be able to withstand the loads which may be exerted on the various parts of the seat, and they must also allow easy control of the pivoting movement of the second frame relative to the first. Usually, mechanisms with epicycloid gear trains are used for this, these being relatively complicated and expensive.
Moreover, the document EP-0,080,633 discloses an adjustable seat framework including two frames articulated to one another, termed respectively first and second frame, the second frame being mounted on the first frame by means of pivots, the first frame including at least one slot termed guide slot and the second frame including at least one slot termed operating slot, associated with said guide slot, the associated guide and operating slots emerging in neighboring parallel planes, said associated guide and operating slots extending longitudinally in non-parallel directions, the adjustable framework further including, for each set of associated guide and operating slots, a roller which penetrates into said associated guide and operating slots at the same time, thus imposing an angular position on the second frame relative to the first frame.
This seat framework includes a relatively complicated locking mechanism for the roller and furthermore it does not have any adjustment mechanism, adjustment of the inclination of the second frame being done by acting manually on this frame directly.